Video/audio (c) copyright 2008, Blender Foundation / www.bigbuckbunny.org
The 14.315 frames of this short film have been download in Full HD 1920×1080 in 2008. In 2021 one scene consisting of 1.182 frames was selected and upscaled 4x to 8k resolution (7680×4320) with the help of Nero AI Image Upscaler. Afterwards Shutter Encoder was used to create an Apple ProRes file from the frame set and the final result was uploaded to YouTube.
You can download Nero AI Image Upscaler from Nero Lab. On an Intel Core i9-9900K it took 6 minutes per frame, so the total upscale the for this scene was 5 days (CPU only, no GPU involved).
The Windows command line for applying Nero AI Image Upscaler to a directory of pictures:
for %%F in ("D:\directoryname\*.png") do NeroAiImageUpscaler.exe --cmd -i %%F -o 4x_%%~nF.png -x 4
Here some details of frame #6.754